Background: Nearly 700,000 US military personnel were deployed to the Persian Gulf in 1990-1991. At least one fourth report negative health consequences including pain, fatigue, and concentration/mood disturbances, known as Chronic Multisymptom Illness (CMI). Although several studies have examined causes of CMI among Gulf War (GW) Veterans, studies of treatment remain limited. Current CMI management includes an integrative approach informed by the biopsychosocial model, with self-management components. Mindfulness-based interventions (MBIs) teach meditation practices intended to enhance present moment awareness and emphasize continued practices after program completion. A widely available mindfulness program is an 8-week program called Mindfulness-Based Stress Reduction (MBSR). Preliminary evidence suggests that MBIs reduce symptoms of CMI. Another widely available self-management program is the Chronic Disease Self- Management Program (CSMP). Specific Aims: Aim 1: Among GW Veterans with CMI, evaluate if MBSR produces greater improvement than CDSMP in symptoms of CMI (pain, fatigue, cognitive failures) at 6-months post-treatment. Aim 2: Assess patient satisfaction and acceptability of either treatment using a mixed methods approach involving (a) qualitative semi-structured interviews of GW Veterans, and (b) a measure of patient satisfaction. Exploratory Aims: Evaluate if MBSR produces greater improvement than CDSMP in symptoms of CMI among non-GW Veterans, as well as other domains of health for both GW Veterans and non-GW Veterans with CMI. Other domains assessed will be depressive symptoms, PTSD symptoms, substance use, and Health-Related Quality of Life (HRQOL). Additional analyses will explore baseline moderators of response. Design: A randomized controlled trial comparing MBSR to CDSMP. Participants: At least 154 GW Veterans with CMI, and up to 154 non-GW Veterans with CMI. Interventions: Group MBSR or an augmented 8-week version of CDSMP. Hypotheses and Analyses: GW Veterans randomized to MBSR will report significantly greater reductions in pain, fatigue, and cognitive failures at 6-month follow-up as compared to CDSMP, and will be more satisfied with care. Implications: If MBSR is shown to be efficacious for symptoms of CMI among GW Veterans, it would support providing MBSR for this population.